This invention relates to crosslinked microparticles defined by the process for producing them by dispersion polymerization in non-aqueous medium without using a polymeric stabilizer, to the associated process and to their uses in coating and moulding compositions, as reactive or non-reactive additives, and as regulators of the rheology and/or reinforcement and/or flexibilization of the host matrix.
Crosslinked microparticles, such as those described in the present invention, are also commonly denoted by the term xe2x80x9cmicrogelsxe2x80x9d. These microgels are essentially characterized by a globular structure (from a new nm to a few microns) of a polymer of very high mass comprising intramolecular crosslinking nodes. Advances in Polymer Science (1998) vol. 136, pp. 139-234 presents a general bibliographical review of microgels, methods for preparing them and a number of applications.
The methods most commonly used for preparing crosslinked microparticles or microgels are, on the one hand, emulsion polymerzation in aqueous medium, and, on the other hand, dispersion polymerization in non-aqueous medium, of compositions of polymerizable compounds comprising, inter alia, a polymerizable compound having the function of a crosslinking agent. In both cases, the polymerization medium is non-solvent for the polymer formed, which precipitates in the form of polymer particles. The essential problem posed for these two preparation methods is the need to stabilize the particles formed during the polymerization in order to protect them against the strong interparticulate interactions which may lead, if they are not controlled, to aggregation and setting to a solid of the particles formed. This stabilization is an essential key parameter in controlling the size of the microparticles, in particular in the range below one micron. Most of the performance quality of the microparticles is directly associated with their specific structure and their size.
The steric stabilizers commonly used to prepare microgels by emulsion or by dispersion are essentially of polymeric structure, well defined and adapted to each case, according to the polymerization medium and the structure of the particle to be stabilized. Macromolecules 1996, 29, 8650-55 in particular describes microgels based on unsaturated polyesters of specific self-emulsifying structure (self-stabilized particles). U.S. Pat. No. 4,206,099 describes crosslinked microparticles obtained by polycondensation in non-aqueous medium, using grafted copolymers as steric stabilizers. U.S. Pat. No. 4,605,720 describes crosslinked acrylic macroparticles obtained by radical-mediated polymerization in dispersion in non-aqueous medium, using polymeric stabilizers.
Among the essential drawbacks of the crosslinked microparticles obtained with stabilizers of polymeric structure, mention may be made of:
the limited availability of the polymeric stabilizer adapted to each individual case as a function of the polymerization medium and the structure of the particle to be stabilized, which often requires the specific prior preparation of the stabilizing polymer in an additional separate step, thus complicating the method for gaining access to the target microparticles.
relatively high concentrations of stabilizing polymer are required to obtain particle sizes of less than one micron, which often poses problems of solubility of the polymer and of viscosity of the corresponding solution with a limitation on the choice of the couples [stabilizing polymer/solvent for the stabilizing polymer and the monomers, and non-solvent for the polymer of the particles formed].
although the high molecular mass and concentration of the stabilizing polymer are favourable to the steric stabilization of the particles formed during the polymerization, this presence of a steric barrier as an outer layer can pose problems of accessibility of the protected structure of the particle, thus creating, depending on the case, a reduction in the efficacy of the reactive functions borne by the particle or incompatibility with respect to the receiving moulding or coating composition, with negative repercussions on the final performance qualities of the coating or of the moulded product.
certain specific microparticle structures are difficult if not impossible to obtain given the fact that the essential presence of the stabilizing polymer automatically limits the possibilities in terms of the structure of the particle (core/shell/effective functionality) and the desirable physicochemical properties of the microparticle relative to the medium and to the intended application.
The present invention proposes to overcome these drawbacks in a simple manner with crosslinked microparticles between 10 and 300 nm in size, preferably between 10 and 200 nm and more particularly from 20 to 100 nm in size, obtained by dispersion polymerization, in non-aqueous medium which is non-solvent for the polymer formed, of a composition of ethylenically unsaturated polymerizable compounds, the said microparticles being characterized in that the said composition comprises:
at least one monomer A, comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization, giving the microparticles formed in the said non-aqueous medium self-stabilization during and after polymerization, without any addition of polymer having the function of a stabilizing agent, either before, during or after polymerization,
at least one compound B comprising at least two ethylenic unsaturations which can undergo radical-mediated polymerization,
and optionally, depending on the case:
at least one compound C comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization, which is different from A
and/or
at least one compound D which is different from A, B and C and comprising at least one ethylenic unsaturation which can undergo radical-mediated polymerization and at least one second reactive function f1 which is other than an ethylenic unsaturation.
The crosslinked microparticles of the present invention are obtained by radical-mediated dispersion polymerization, in non-aqueous medium which is non-solvent for the polymer formed, of a composition of ethylenically unsaturated polymerizable compounds comprising the compounds A, B, C and D as defined above, in the absence of any added polymer for stabilizing the microparticles, formed during the polymerization, either before, during or after the dispersion polymerization.
The compounds A are necessarily monomers with only one ethylenic unsaturation which can undergo radical-mediated polymerization, while the compounds B, C and D can be monomers and/or oligomers. These oligomers have molecular masses {overscore (Mn)} of less than 2500 and preferably less than 1500.
The monomers A giving the microparticles formed self-stabilization as defined above can be selected from monomers containing only one ethylenic unsaturation which can undergo radical-mediated polymerization, with a molecular mass {overscore (Mn)} of less than 600 and preferably less than 400, containing only one polymerizable ethylenic unsaturation selected from (meth)acrylates, maleates and vinyls and borne by a linear or branched aliphatic group or a substituted or unsubstituted monocyclic or polycyclic alicyclic group which can optionally bear at least one reactive function f2 which is different from the polymerizable ethylenic unsaturation. In general, the stabilizing function of the monomer A is associated with an adequacy of the solubility parameter of this monomer relative to that of the polymerization medium and that of the polymer formed. The term xe2x80x9c(meth)acrylatexe2x80x9d should be interpreted throughout as xe2x80x9cacrylate and/or methacrylatexe2x80x9d.
Preferably, the monomers A have a chemical structure corresponding to the general formula (I) below:
CH2xe2x95x90CR1xe2x80x94Xxe2x80x94(R2xe2x80x94Y)kxe2x80x94Rxe2x80x83xe2x80x83(I)
with R1=H, CH3 
X=ester xe2x80x94(Cxe2x95x90O)Oxe2x80x94, amide xe2x80x94(Cxe2x95x90O)N(R3)xe2x80x94
Y=ester xe2x80x94O(Oxe2x95x90C)xe2x80x94, amide xe2x80x94(R3)N(Cxe2x95x90O)xe2x80x94, urethane xe2x80x94O(Oxe2x95x90C)NHxe2x80x94
R2=C2-C6 alkylene radical which can be substituted with functional groups such as OH
R3=C1-C6 alkyl, H
k=0 or 1
R=linear or branched C8-C22 alkyl or alkenyl radical or C8-C22 aralkyl radicals substituted on the aromatic ring, or substituted or unsubstituted C6-C22 acyclic, monocyclic or polycyclic radical which can comprise a reactive function f2 selected from: carboxylic acid or anhydride, hydroxyl, epoxy, isocyanate, silane.
The preferred monomers A of formula (I) correspond to R chosen from: isobornyl, lauryl, octadecyl, isodecyl, tridecyl, docosanyl, dicyclopentadienyl, cyclohexyl or a C8-C22 alkyl or cycloaliphatic group bearing a carboxylic acid or anhydride, hydroxyl, epoxy, isocyanate or silane reactive function f2. As examples of monomers A bearing a carboxylic acid function f2, mention may be made of mono(meth)acrylated derivatives of succinic anhydride substituted with a linear or branched C6-C22, preferably C6-C18, alkyl or alkenyl, obtained by reacting the alkyl-substituted or alkenyl-substituted anhydride with a hydroxyalkyl (meth)acrylate containing a C2-C6 and preferably C2 or C3 hydroxyalkyl group. As examples of monomers A bearing a hydroxyl function f2, mention may be made of mono(meth)acrylated derivatives of hydroxystearic acid, obtained by reaction of hydroxystearic acid with glycidyl methacrylate or Cardura E10 (meth)acrylate. An epoxy function f2 can be introduced, for example epoxidized dicyclopentadiene (meth)acrylate, epoxidized vinylnorbornene (meth)acrylate or (meth)acrylates comprising a cycloaliphatic epoxy, as described in WO 98/28286, or an epoxidized unsaturated fatty acid (meth)acrylate. A function f2 can be introduced with a mono(meth)acrylate derived from the reaction between a cycloaliphatic or aliphatic C6-C12 diisocyanate with a hydroxyalkyl (meth)acrylate containing a C2-C6 alkyl.
The molar content of monomers A in the final microparticles obtained can range from 5% to 99% depending, on the one hand, on the nature of the monomer A, and, on the other hand, on the role fulfilled either as a simple monomer for stabilizing a variable composition based on compounds B, C and D, or as both a stabilizing monomer and a predominant base component of the target microparticles. Consequently, the molar percentage will be limited only by the desired performance qualities of the microparticles to be obtained. In general, the self-stabilizing effect is sufficient in a range extending from 5 mol % to 80 mol % and as a function of the monomer A chosen. The monomers A have, by the definition of their function, the specificity of preferentially binding to the outer layer of the microparticles and more specifically to the surface of these microparticles. This point is important in particular when the monomer A bears a reactive function f2 as defined above. The reason for this is that, in this case, the specificity of the monomer A allows it to bind the reactive function f2 specifically to the surface of the microparticle, thus even more significantly enhancing its accessibility and its overall reactivity relative to the same functions borne by the compounds D bearing functions f1, these functions f1 being distributed randomly throughout the volume of the microparticle, with a less ready accessibility of the functions in the core of the microparticle than at the surface. If more than one monomer A bearing functions f2 is used, the different functions f2 should not react together or with the functions f1 of the compounds D, during the polymerization.
The compounds B comprise at least two ethylenic unsaturations and serve as agents for crosslinking the microparticles formed. B is an essential component of the composition of the polymerizable compounds. They are essentially ethylenically multifunctional monomers and/or oligomers with a functionality, in terms of unsaturations which can undergo radical-mediated polymerization, of at least two. In the case of the monomers, the functionality, as defined above, can preferably range from 2 to 6. As examples of such monomers, mention may be made of: di(meth)acrylates of ethylene glycol, of propylene glycol, of butanediol, of 2-methylpropanediol, of neopentyl glycol, of hexanediol, of zinc and/or of calcium or substituted or unsubstituted divinylbenzenes, tri(meth)acrylates of glycerol, of trimethylolpropane and/or of alkoxylated derivatives, tri- or tetra(meth)acrylates of pentaerythritol and penta- or hexa(meth)acrylates of dipentaerythritol. The multifunctional oligomers have a functionality which can range from 2 to 50 and preferably from 2 to 20 and a molecular mass {overscore (Mn)} of less than 2500, preferably less than 1500. The functionality and {overscore (Mn)} are set as a function of the desired crosslinking density. The lower the value of {overscore (Mn)} and the higher the functionality and the higher the crosslinking density of the microparticles. As examples of such oligomers, mention may be made of (meth)acrylic esters of polyol oligomers based on polyethers, comprising ether units chosen from oxyethylene and/or oxypropylene and/or oxytetramethylene, or based on saturated polyesters, or based on unsaturated polyurethanes or polyesters, or (meth)acrylated acrylic oligomers which can be obtained, for example, either by (meth)acrylation of (meth)acrylic copolymers based on glycidyl methacrylate with (meth)acrylic acid, or by (meth)acrylation of (meth)acrylic copolymers based on (meth)acrylic acid with glycidyl methacrylate.
The molar content of the compound B can range from 0.02% to 30% and preferably from 0.5% to 15%. The limitation of this content is important since, beyond a limiting content, the probability of chemical bridging between microparticles becomes significant, with, as a consequence, a large risk of destabilization, aggregation and sedimentation of the microparticles.
The compounds C are monomers different from the monomers A as defined above and/or oligomers, bearing only one ethylenic unsaturation which can undergo radical-mediated polymerization, and are components for adjusting the base composition as a function of the intended properties of the microparticles which can vary and be adapted according to each specific application. They are preferably selected from (meth)acrylic monomers such as methyl, ethyl, propyl, butyl, tert-butyl or 2-ethylhexyl (meth)acrylates, or vinylaromatic monomers such as styrene or vinyltoluenes or vinyl esters such as vinyl acetate or (meth)acrylated oligomers with an {overscore (Mn)} of less than 2500 and more particularly less than 1500, such as (meth)acrylates of monofunctional alcohol oligomers. The preferred (meth)acrylate oligomers are polyalkoxylated monoalcohol (meth)acrylates, comprising alkoxy units chosen from oxyethylene and/or oxypropylene and/or oxytetramethylene, or (meth)acrylates derived from monoalcohols based on polycaprolactone, or on polyesters or polyurethanes. The presence of these compounds is optional depending on the structure and the performance qualities desired for the microparticles to be obtained. Monomers or oligomers of this type can adjust the mechanical performance qualities of the microparticles in terms of hardness or flexibility of the particle core as a function of the Tg temperatures corresponding to the glass transition. For example, a combination of structures with a high Tg, such as methyl methacrylate and/or styrene, with structures with a low Tg, such as butyl acrylate, makes it possible to obtain, as a function of the adjusted proportions, microparticles with a predominant nature ranging from the hardest to the softest. This type of structure is particularly advantageous in the reinforcement of a soft matrix or the flexibilization of a hard matrix or in the search for a hardness/flexibility compromise for applications in coatings or moulding compositions, in particular thermosetting compositions. Their molar content can range from 0 to 80% depending on the desired structure of the final microparticle.
The compounds D are monomers, different from A or B or C, and/or oligomers, different from B or C, bearing at least one ethylenic unsaturation which can undergo radical-mediated polymerization and at least one second reactive function f1 which is different from the ethylenic unsaturation. These functionalized monomers or oligomers bear reactive functions f1 selected from: carboxylic acid or anhydride, hydroxyl, epoxy, isocyanate, silane, amine or oxazoline. Without limitation, the following examples of possible compounds D may be mentioned:
when the function f1 is a carboxylic acid: (meth)acrylic, maleic, fumaric or itaconic acid
when f1 is an anhydride function: maleic or itaconic anhydride
when f1 is a hydroxyl: hydroxyalkyl (meth)acrylates containing a C2-C4 hydroxyalkyl such as hydroxyethyl, hydroxypropyl or hydroxybutyl, or mono(meth)acrylates of polycaprolactone or of diols, such as: polyether diols comprising ether units chosen from oxyethylene and/or oxypropylene and/or oxytetramethylene, polyester diols or polyurethane diols, with an {overscore (Mn)} of less than 2500 and preferably less than 1500
when f1 is an epoxy function: glycidyl methacrylate or an alkoxylated glycidyl (meth)acrylate as described in WO 98/28287
when the function f1 is an isocyanate: isocyanatoethyl (meth)acrylate or the mono(meth)acrylate of a urethane isocyanate derived from the condensation of a (C2-C6)hydroxyalkyl (meth)acrylate with an aromatic diisocyanate such as toluene diisocyanate (TDI)
when f1 is a silane function, it can be used in the form of trialkyl- or trialkoxysilane borne by a monomeric or oligomeric (meth)acrylic derivative
when f1 is an amine function: tert-butylaminoethyl methacrylate or dimethylaminoethyl methacrylate
when f1 is an oxazoline function: oxazoline (meth)acrylates and more particularly 2-(5-methacryloylpentyl)-1,3-oxazoline.
In general, the functions f1 borne by at least one compound D can be different, but they should not react with each other or with any functions f2 borne by the monomers A, during the polymerization.
The choice of the compound D and of its reactive function and the molar content will depend essentially on the reactive system of application and on the composition and functionality of this system. The molar content can thus range from 0 for unreactive systems to 80% for highly reactive systems.
It is obvious to those skilled in the art that these functions should not interact with the polymerization medium, in order for these reactive functions to be preserved. One means of preserving the functions f1 liable to interact with the polymerization medium is to block the function f1 with a blocking agent, with possible deblocking of f1 after polymerization, in the same context as a chemical modification of the functions f1 after the polymerization step. Such a preventive blocking and subsequent deblocking is well known to those skilled in the art.
The functions f1 borne initially by the compound D and/or the functions f2 which may be borne by the monomer A can be modified after polymerization into functions f3 and f4, respectively, by chemical reaction in one or more steps with suitable reagents. For example, the introduction of a final (meth)acrylate function f4 may take place either starting with an epoxy function f1 by reaction with (meth)acrylic acid, or starting with a carboxylic acid f1 by reaction with glycidyl (meth)acrylate or hydroxyethyl (meth)acrylate. These latter reactions can also be used to introduce acrylic functions f3 specifically at the surface of the microparticle, starting with possible initial carboxylic acid functions f2. These chemical modifications may be partial or total and adapted to the application compositions and the optional crosslinking mechanism used. A double functionality may be sought in a dual crosslinking system involving two crosslinking mechanisms, such as, for example, acrylate and epoxy for radical-mediated and cationic crosslinking mechanisms or for radical-mediated and condensation crosslinking mechanisms.
Thus, the initially functionalized microparticles f1 and/or f2, after a suitable chemical modification of the functions f1 and/or f2, can bear, at least partially, functions f3 and/or f4 selected from (meth)acrylates, vinyls, esters or amides containing a C12-C22 unsaturated fatty chain, maleates and/or maleimides, esters derived from allylic alcohols or cycloaliphatic unsaturations based on dicyclopentadiene or on a tetrahydrophthalic ring system, or carboxylic acid salts by at least partial neutralization of a carboxylic acid.
The molar composition and the functionality of the microgels can be adjusted depending on the desired application. Depending on the nature and proportions of the polymerizable compounds A, B, C and D, the microparticles obtained, with a size ranging from 10 to 300 nm, can, after recovery, be in the form of liquid, wax or solid powder with glass transition temperatures and/or melting points that are variable and adjustable as a function of the needs of the desired application.
Preferably, the composition of the ethylenically unsaturated polymerizable compounds comprises:
5-99 mol % of at least one monomer A comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization, as defined above
0.02-30 mol % and more particularly from 0.5 to 15 mol % of at least one compound B bearing at least two polymerizable ethylenic unsaturations
and optionally, depending on the case:
0-80 mol % of at least one compound C which is different from A, comprising only one polymerizable unsaturation
0-80 mol % of at least one compound D which is different from A, B and C, comprising at least one polymerizable ethylenic unsaturation and at least one second reactive function f1 which is different from the ethylenic unsaturation,
with the molar percentages of A and B and optionally of C and/or D chosen within the defined limits, such that their sum is equal to 100% relative to the composition of all of the polymerizable compounds present.
More particularly, in the case of microparticles with an initial epoxy function f1 which can be chemically modified, after polymerization, into function f3 containing ethylenic unsaturation, the composition of the polymerizable compounds can comprise:
0-30 mol % of octadecyl (meth)acrylate and/or
5-80 mol % of isobornyl (meth)acrylate as monomer A
0.02-30 mol % of hexanediol di(meth)acrylate as compound B
0-50 mol % of styrene and/or of methyl and/or butyl or tert-butyl (meth)acrylate, as compound C
0-50 mol % of glycidyl (meth)acrylate as compound D,
with the molar percentages of A, B, C and D selected such that their sum is equal to 100% of the composition of the polymerizable compounds and with the glycidyl reactive functions possibly being at least partially modified by reaction with an ethylenically unsaturated acid or anhydride. As examples of such ethylenically unsaturated acids, mention may be made of (meth)acrylic acids and maleic acid or anhydride, itaconic anhydride and fumaric acid.
One specific microparticle structure can be obtained if the polymerization is carried out in several successive steps by continuous or batchwise addition, i.e. in a single portion, of the composition of each step which may be identical or different. The composition of each step thus comprises compounds A, B and optionally C and/or D with the same essential respective functions for stabilization, crosslinking, composition adjustment and functionalization as when the polymerization is carried out in a single step. Depending on the composition of each step, the microparticle structures thus obtained can be of multilayer type with a microparticle core whose composition is different from that of the outer layer.
A second subject of the present invention is a process for preparing crosslinked microparticles between 10 and 300 nm in size, comprising a step of dispersion polymerization, in non-aqueous medium which is non-solvent for the polymer to be formed, of a composition of ethylenically unsaturated polymerizable compounds, characterized in that the polymerization step is carried out on a composition comprising:
at least one monomer A, comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization and giving the microparticles formed in the said non-aqueous medium self-stabilization during and after the polymerization, without any addition of polymer having the function of a stabilizing agent, either before, during or after the dispersion polymerization, with the said monomer A preferably being bound to the outer layer and more preferably to the surface of the microparticles thus obtained
at least one compound B comprising at least two polymerizable ethylenic unsaturations
and optionally, depending on the case:
at least one compound C, comprising only one polymerizable ethylenic unsaturation, which is different from A and/or
at least one compound D which is different from A, B and C, comprising at least one polymerizable ethylenic unsaturation and at least one second reactive function f1 which is different from the ethylenic unsaturation.
Preferably, the compound A used for this process is defined by the general formula (I) below:
CH2xe2x95x90CR1xe2x80x94Xxe2x80x94(R2xe2x80x94Y)kxe2x80x94Rxe2x80x83xe2x80x83(I)
with R1=H, CH3 
X=ester xe2x80x94(Cxe2x95x90O)Oxe2x80x94, amide xe2x80x94(Cxe2x95x90O)N(R3)xe2x80x94
Y=ester xe2x80x94O(Oxe2x95x90C)xe2x80x94, amide xe2x80x94(R3)N(Cxe2x95x90O)xe2x80x94, urethane xe2x80x94O(Oxe2x95x90C)NHxe2x80x94
R2=C2-C6 alkylene radical which can be substituted with functional groups such as OH
R3=C1-C6 alkyl, H
k=0 or 1
R=linear or branched C8-C22 alkyl or alkenyl radical or C8-C22 aralkyl radicals substituted on the aromatic ring, or substituted or unsubstituted C6-C22 acyclic, monocyclic or polycyclic radical which can comprise a reactive function f2 selected from: carboxylic acid or anhydride, hydroxyl, epoxy, isocyanate, silane.
The preferred monomers A of formula (I) correspond to R chosen from: isobornyl, norbornyl, lauryl, tridecyl, isodecyl, octadecyl, docosanyl, dicyclopentadienyl, cyclohexyl or a linear or branched alkyl or alkenyl group or a substituted aralkyl group or a C8-C22 cycloaliphatic group bearing a carboxylic acid or anhydride, hydroxyl, epoxy and/or isocyanate reactive function f2. As examples of monomers A bearing a carboxylic acid function f2, mention may be made of mono(meth)acrylated derivatives of succinic anhydride substituted with a linear or branched C6-C22, preferably C6-C18, alkyl or alkenyl, obtained by reacting the alkyl-substituted or alkenyl-substituted anhydride with a hydroxyalkyl (meth)acrylate containing a C2-C6 and preferably C2 or C3 hydroxyalkyl group. As examples of monomers A bearing a hydroxyl function f2, mention may be made of mono(meth)acrylated derivatives of hydroxystearic acid, obtained by reaction of hydroxystearic acid with glycidyl methacrylate or Cardura E10 (meth)acrylate. An epoxy function f2 can be introduced, for example with epoxidized dicyclopentadiene (meth)acrylate, epoxidized vinylnorbornene (meth)acrylate, or an epoxidized unsaturated fatty acid (meth)acrylate. A function f2 can be introduced with a mono(meth)acrylate derived from the reaction between a cycloaliphatic or aliphatic C6-C12 diisocyanate with a hydroxyalkyl (meth)acrylate containing a C2-C6 alkyl. In any case, this process does not require the addition of a stabilizing polymer to stabilize the microparticles in dispersion, either before, during or after the polymerization. In general, the self-stabilizing effect is sufficient within a range extending from 5 mol % to 80 mol % as a function of the monomer A chosen. Needless to say, when the monomer A is alone in the presence of the compound B, in this case the molar content can range up to 99 mol %.
The compounds B, C and D of this process which may be monomers and/or oligomers are those already specified for the microparticles obtained. When at least one monomer A bears at least one function f2 and at least one compound D bears at least one function f1, the choice of A and D is made such that there is no reaction between these functions during the polymerization.
The solvent used for this process is an organic solvent or a mixture of organic solvents selected from C6-C10 alkanes such as hexanes, heptanes and more particularly n-heptane, cyclohexane, octanes, nonanes and/or C3-C5 alkanols such as isopropanol, butanol or pentanol. Mixtures of apolar solvents such as heptane with polar solvents such as isopropanol are preferred to adjust the solvating power of the medium relative to the polymerizable compounds, on the one hand, and the non-solvating power of the medium, which becomes a precipitation medium relative to the polymer formed, on the other hand. Moreover, this solvent medium should be chemically inert with respect to the reactive functions f1 or f2 or other functions present. The weight ratio between the C6-C10 alkane and the C3-C5 alkanol can range from 0/100 to 75/25 and more particularly from 25/75 to 50/50. This remains preferred in particular when this mixture is based on n-heptane or cyclohexane, on the one hand, and on isopropanol or butanol, on the other hand.
The weight ratio between the sum of the compounds A, B, C and D, on the one hand, and the solvent or mixture of solvents, on the other hand, can range from 10/90 to 50/50 and preferably from 15/85 to 30/70. This ratio is one of the parameters of the process for controlling the size of the microparticles. The more the dilution increases, the greater the tendency of the size of the microparticles to decrease.
The dispersion polymerization of the ethylenically unsaturated compounds is carried out via a radical route by adding a radical initiator commonly used for this type of polymerization, which is suited to the medium. The polymerization temperature is adapted to the decomposition temperature of the radical initiator chosen and to the boiling point of the solvent medium used and may vary in general, as a function of the initiator and the solvent medium used, from 20xc2x0 C. to 150xc2x0 C. As examples of initiators, mention may be made of: azo derivatives such as azobisisobutyronitrile (AIBN) and derivatives, peroxides and hydroperoxides or any other initiator system which is soluble in the polymerization medium and known to those skilled in the art. More particularly, these initiators can be functionalized with a reactive function f5 such as hydroxyl or carboxyl, such as, for example, hydroxylated or carboxylated azo derivatives. In this case, the microparticles obtained will be at least partially functionalized with the functions f5. Moreover, other radical initiators can be used for a so-called xe2x80x9ccontrolledxe2x80x9d or xe2x80x9clivexe2x80x9d radical-mediated polymerization, as described in Comprehensive Polymer Science, vol.3, pp. 141-146, Pergamon, London, 1989. Similarly, chain-transfer agents such as mercaptans can be combined with the initiator in order better to control the molecular masses. The polymerization time will depend on the nature and content of initiator and on the polymerization temperature. The usual initiator content can range from 0.05 to 5% by weight relative to the sum of the polymerizable compounds A, B, C and D.
According to a first embodiment of this batch process, all of the polymerizable compounds A, B, C and D are added, with stirring, from the start in the reactor containing all of the solvent and maintained at the polymerization temperature. The monomers can also be added in solution form in some of the polymerization solvent. The initiation of the polymerization takes place, with vigorous stirring, by gradual addition of the radical initiator chosen, which is soluble in the polymerization medium. After the end of the addition of the initiator, the polymerization proceeds for a time which can range from 1 h to 8 h depending on the temperature, the nature and content of the initiator, and the nature and overall concentration of polymerizable compounds. The self-stabilized microparticles formed in the polymerization medium can be recovered either after successive steps of precipitation, by adding a non-solvent such as an alcohol in a proportion ranging from 2/1 to 5/1 by weight relative to the dispersion, and then of filtration and drying, or by a single step for evaporating off the dispersion-medium solvent, preferably under a reduced pressure of from 10 to 30 mbar.
The final size of the microparticles obtained ranges from 10 to 300 nm and preferably between 10 and 200 nm and more particularly from 20 to 100 nm as a function of the dilution of the polymerizable compounds and the nature and molar ratio of the monomer A chosen. The size of the microparticles can be reduced by increasing the content of monomer A and/or increasing the molar mass of the monomer A whose chemical structure is of similar formula and/or increasing the level of dilution of the polymerizable compounds and/or increasing the precipitating power of the polymerization medium by adjusting the nature and/or composition of the polymerization-medium solvent. The essential advantage of this process and of its various embodiments is its simplicity and its flexibility in the preparation of a large variety of microparticle structures, by simply varying the nature and proportions of the compounds A, B, C and D.
According to a second embodiment of this process, it comprises one or more successive steps of continuous and/or batchwise polymerization, characterized respectively by an addition of polymerizable compounds continuously or in a single portion per step concerned, respectively. When the process comprises more than one step of batchwise and/or continuous polymerization, the composition of the polymerizable compounds may be identical or different from one step to another. Thus, it is possible to prepare very specific microparticle structures of multilayer type as a function of the composition of the polymerizable compounds in each step and as a function of the chronological order of each continuous or batchwise step.
A continuous embodiment of this process is particularly preferred when the composition of the polymerizable compounds comprises at least one of the compounds A, B, C or D which has reactivity that is significantly different from the average reactivity of the polymerizable compounds. This is particularly preferred when the monomer A has a reactivity that is significantly different from the average reactivity of the other polymerizable compounds. This reactivity may be characterized by the rate of consumption of the polymerizable unsaturations of these compounds. This is the case, for example, if the monomer A is a methacrylate and the other polymerizable compounds are acrylates. A batchwise process may also be envisaged when the monomer A has a reactivity that is significantly different from the average reactivity of the polymerizable compounds if the choice of at least one second monomer A is well adapted such that the reactivities of these two monomers encompass the average reactivity of the other polymerizable compounds.
When the composition of the polymerizable compounds comprises at least one monomer A bearing a function f2 and/or at least one monomer D bearing a function f1, the process as described above can comprise, after the polymerization step, an additional step of chemical modification of the function f2 and/or of the function f1. This chemical modification step can take place, depending on the case, either before recovery of the microparticles by evaporating off the polymerization solvent, or after recovery of these microparticles, in which case the chemical modification can take place, depending on the case, either in bulk if the viscosity allows it at the modification temperature, or in solution in a solvent which is different from the polymerization solvent if the latter is unsuitable, as regards the temperature or the chemical inertness. As a preferred example of a chemical modification, mention may be made of the acrylation of reactive functions such as: epoxy and hydroxyl with acrylic and methacrylic acid or maleic or itaconic acid or anhydride, or carboxylic acid or anhydride with glycidyl methacrylate or hydroxyethyl methacrylate or hydroxyethyl acrylate or oxazoline (meth)acrylate. For example, the acrylation can take place in solution containing about 30-60% of dispersed microparticles, in the presence of esterification catalysts such as chromium(III) diisopropyl salicylate, chromium(III) ethyl hexanoate, ethyltriphenylphosphonium bromide or tertiary amines. When the modified function is a vinyl function, OH functions are modified with a vinyl azlactone such as 2-vinyl-4,4-di-methylazlactone, or a vinyl isocyanate such as m-isopropenyl, dimethyl or benzyl isocyanate.
One variant of this process can comprise, before the polymerization step, a step of dispersion, in the non-aqueous medium, of organic or inorganic microparticles which are insoluble in this medium, followed by a polymerization step as described above. In this case, the organic or inorganic microparticles in dispersion have sizes adapted to that of the final microparticles to be obtained. The predispersed microparticles can be chosen from organic or inorganic pigments or organic or inorganic fillers or additives or previously prepared microparticles as already described which are insoluble in the dispersion medium. This process variant allows an at least partial, but simple and practical coating or encapsulation of the predispersed microparticles, with the aim, for example, of improving their dispersibility in other dispersion media (aqueous or organic media) or of improving their compatibility in recipient matrices for coating, moulding or composite compositions.
A third subject of the invention relates to the use of the microparticles as defined above in coating or moulding compositions, as sole or predominant reactive components or as reactive or unreactive additives. When the microparticles constitute a sole or predominant reactive system in the composition, the content of mutually reactive microparticles constituting the system can range up to 100%. When the microparticles are used as reactive or unreactive additives, the preferred content of microparticles can range from 0.5 to 50% and more particularly from 1 to 30% by weight relative to the organic composition of the coating or moulding.
Among the specific advantages of these microparticles which are recalled are markedly improved compatibility and, depending on the case, reactivity, without any limitation forced by a stabilizing polymer imposed by the fact of its availability.
Moreover, their particular structure obtained by virtue of the specific process used gives them a self-dispersibility and self-stabilizing nature in a solvent medium which is comparable to that of the polymerization. Similarly, this process makes it possible to obtain crosslinked microparticles which are highly monodisperse in terms of size, this being important in order to obtain specific Theological and viscoelastic performance qualities for certain applications in the field of coating compositions, moulding compositions or composites.
In general, these microparticles can be used in crosslinkable or non-crosslinkable coating or moulding compositions in order:
to reduce the viscosity of these compositions, allowing better wetting and better application to the substrates to be coated and, moreover, compositions with a higher solids content and consequently a lower content of volatile organic compounds
to better control, by specific application, the rheology of these compositions by adjusting the structure of the microparticles
to reinforce or plasticize the matrix as a function of the compatibility and the Tg of the microparticle relative to the host matrix.
The microparticles as unreactive additives can have functions selected from f1, f2, f3 and f4 as defined above which, while being chemically inert with respect to the host composition, can substantially improve the compatibility of the microparticle with respect to the host matrix by means of favourable physicochemical interactions.
In the case of microparticles used as reactive additives, their reactive functions are selected and adapted or modified to react with the reactive functions of the host crosslinkable composition or with each other. For example, in the case of a composition which can undergo radical-mediated, thermal or photochemical crosslinking, containing ethylenically unsaturated monomers and/or monofunctional or multifunctional oligomers, the microparticles, after chemical modification following the polymerization step, will preferably be polyunsaturated. Multi-epoxidized or multihydroxylated reactive microparticles will be adapted for coating compositions of epoxides which can be photocrosslinked cationically in the presence of cationic photoinitiators such as triarylsulphonium or diaryliodonium salts. Multi-epoxidized or multicarboxylated reactive microparticles will be adapted for the crosslinking of coating or moulding compositions based on epoxides and on polyamines or on dicarboxylic acid anhydride or carboxylated acrylic copolymers. Similarly, partially neutralized multicarboxylated microparticles can serve as water-dispersible or water-soluble microparticles depending on the degree of neutralization and can be used in coating compositions based on aqueous dispersions of reactive or unreactive polymers. This water-dispersibility or water-solubility nature can also be imparted by a compound C and/or B selected, respectively, from the mono- and diacrylates or methacrylates of polyether diols such as polyethylene glycol with an {overscore (Mn)} of less than 1500. In particular, microparticles thus water-dispersible or water-soluble bearing acrylate or methacrylate functions after partial modification of their initial functions f1 or f2 can be used in photocrosslinkable coatings based on aqueous dispersions of polymers, preferably acrylic polymers. When microparticles are used as reactive additives on account of their high functionality, they have a function as a genuine crosslinking agent and reactivity activator for the system concerned. The effect on the mechanical performance qualities of the coating or of the moulded product is reflected either by an increased reinforcement of the matrix or by a combined effect of increased reinforcement and flexibility, as a function of the functionality, compatibility and Tg of the microparticle chemically grafted to the host matrix, the microparticle behaving like a grafted or ungrafted and hard or flexible microfiller.
Moreover, depending on the nature of the reactive functions, in particular in the case of unsaturations which can undergo radical-mediated crosslinking, these microparticles can be used alone or as a predominant component of a crosslinkable matrix. This also remains valid for other microparticles bearing functions f1 and/or f2 and/or f3 and/or f4 which are different from each other but mutually reactive, thus possibly producing a reactive two-component system, this system merely being the sole or predominant component of the composition. This is particularly advantageous in the case of microparticles which can be used as crosslinkable powders for coating or moulding systems.
The coating or moulding compositions concerned can find applications in very varied fields, such as protective varnishes, paints, adhesives, inks, composites and matrices for composites, powders for moulding or for coatings, or moulded products. In this respect, common additives and/or fillers may be present depending on the intended application.